The present invention relates to a lithium secondary battery using a solid electrolyte, and a halide having a spinel structure or a spinel analogous structure as an active material.
Recently, with the development of portable appliances such as personal computers and portable telephones, demands for batteries as an electric power source are extremely large. Particularly, since lithium has a small atomic weight and is a material having large ionization energy, a lithium battery is intensively researched in various fields as a battery which can obtain high energy density.
In electrodes of a battery, charge-transfer occurs between an ion moving in an electrolyte and a current flowing in an outer circuit. Therefore, as an active material in a lithium battery, a mixed conductor is preferably used which has lithium ion conductivity together with electron conductivity. One example of such a lithium ion-electron mixed conductor includes various compounds having a spinel structure. A compound of a spinel structure has a three-dimensional diffusion path for a lithium ion and has a preferable structure for transfer of a lithium ion.
Further, when a battery is charged and discharged, the amount of a lithium ion in an active material changes, and with this change, the volume of the active material also changes. When this voluminal change is too large, deteriorations in battery properties are caused such as a deterioration in contact condition between active materials during operation of a battery. LiCoO2 used presently as a positive electrode active material for a lithium secondary battery has a two-dimensional structure in which a lithium ion is present between layers formed by CoO2. When the amount of lithium ion s between these layer s changes, the interlayer distance changes significantly. Whereas, a compound having a spinel structure has a three-dimensional structure, and when it is utilized for an active material of a battery, such a voluminal change concurrent with charging and discharging can be suppressed.
As the compound having a spinel structure that has been investigated as an active material for a lithium battery. there are exemplified oxides such as LiMn2O4 and Li4/3Ti5/3O4, and sulfides such as CupTi2S4.
Additionally, as the lithium-containing compound having the same spinel structure, there have been reported halides such as chlorides and bromides. These are, for example, Li2MnCl4 (C. J. J. van Loon and J. de Jong, Acta Crystallog raphica B, 24, 1968 (1982)), Li2FeCl4 (R. Kanno, Y. Takeda, A. Takahashi, O. Yamamoto, R. Suyama, and S. Kume, Journal of Solid State Chemistry, 72, 363 (1988)), Li2CrCl4 (R. Kanno, Y. Takeda, A. Matsumoto, O. Yamamoto, R. Suyama, and S. Kume, Journal of Solid State Chemistry, 75, 41 (1988)), Li2CoCl4 (R. Kanno, Y. Takeda, and O. Yamamoto, Solid State Ionics, 28, 1276 (1988)), Li2xe2x88x922pMn1+pBr4 (R. Kanno, Y. Takeda, O. Yamamoto, C.Cros, W. Gang, and P. Hagenmuller, Journal of Electrochemical Society, 133, 1052 (1986)), and the like.
However, since these lithium-containing halides having a spinel structure has a high ion bonding property, when an electrolyte prepared by dissolving a supporting electrolyte in a usual organic solvent is used, the halides are easily dissolved in the electrolyte. That is, it was difficult to use the above-mentioned halides as an active material in a lithium battery.
The present invention solves the above-mentioned conventional problems. Specifically, the object of the present invention is to provide a lithium secondary battery using a lithium-containing halide having a spinel structure or a spinel analogous structure.
The present invention relates to a lithium secondary battery comprising a chargeable and dischargeable positive electrode, a chargeable and dischargeable negative electrode and a lithium ion conductive inorganic solid electrolyte, wherein at least one of the positive electrode and negative electrode comprises a lithium-containing halide having a spinel structure or a spinel analogous structure.
The above-mentioned lithium-containing halide is preferably represented by the formula Li2xe2x88x922pxe2x88x92qMe1+pX4, wherein Me is at least one transition metal element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni and Cu, X is at least one halogen element selected from the group consisting of F, Cl, Br and I, and 0xe2x89xa6pxe2x89xa60.5 and 0xe2x89xa6qxe2x89xa62xe2x88x922p.
The above-described lithium-containing halide is further preferably represented by Li2MeX4, wherein Me is Fe, Mn or Co.
The above-described lithium ion conductive inorganic solid electrolyte is preferably a sulfide-based lithium ion conductive inorganic solid electrolyte.
The above-described lithium ion conductive inorganic solid electrolyte is preferably a silicon-containing sulfide-based lithium ion conductive inorganic solid electrolyte and preferably contains oxygen in an amount of 5 to 70 mol per 100 mol of silicon.
By use of a lithium ion conductive inorganic solid electrolyte as an electrolyte, there can be obtained a rechargeable lithium battery using as an active material a lithium-containing halide having a spinel structure or a spinel analogous structure.